Letrel Bighetty-Castel, 5, left, Troi Castel-Lapansee, 3, centre, and Robert Castel-Lapansee Jr., 4, grin for a photo taken hours before they died in a fire in Pukatawagan, Man., on March 10. (Family photo)A fire that killed three young boys and a man in Pukatawagan, Man., in March was caused by careless disposal of smoking materials, the fire commissioner's office said Monday.

Two brothers — Troi Castel-Lapansee, 3, and Robert Castel-Lapansee Jr., 4 — and their cousin, Letrel Bighetty-Castel, 5, died of smoke inhalation in the fire in the remote community, located about 700 kilometres northwest of Winnipeg

Simon Nicholas, 57, died almost three weeks after the fire in a Winnipeg hospital, also due to smoke inhalation.

The fire broke out on the afternoon of March 10 in a house trailer on the reserve. Local residents and firefighters rushed to the scene and saved Nicholas, but heavy flames prevented them from reaching the boys trapped inside.

The boys were the grandchildren of Shirley Castel, the chief of the Mathias Colomb Cree Nation, which includes the community of Pukatawagan. At the time of the fire, Castel was in The Pas, Man., where her daughter Selena, the mother of the two brothers, was giving birth.

Nicholas had been babysitting the boys, who called him "Grandpa-Uncle," while their father worked at a nearby health centre. Their cousin had come by for a visit.